In the art, a number of different DC-AC converter types have been used for connecting photovoltaic (PV) elements, such as solar panels, to existing electrical grids. Examples of prior art converter types for converting DC voltage produced by solar panels into AC voltage are e.g. string converters, power optimizers and microinverters. The respective type of converter is associated with certain advantages and drawbacks. For instance, the string converters have a high conversion efficiency but are poor when it comes to partial shading harvesting, while the power optimizers perform well at partial shading harvesting but are less conversion effective than the string converters and more expensive. Finally, microinverters generally perform well and are versatile but also more expensive than both the string converter and the power optimizer.
A further DC-AC converter that has proven useful in solar panel applications is the cascaded full-bridge converter, also referred to as the cascaded H-bridge converter or chain link converter. The cascaded H-bridge converter consists of a number of full-bridge converters connected in cascade, i.e. in series. A converter fed with a DC voltage VDC is able to produce a 3-level output consisting of the voltage levels +VDC, zero and −VDC. The output of each converter is added such that a multilevel waveform is formed. A circuit consisting of N cascaded H-bridge converters can produce a voltage waveform with 2N+1 voltage levels, with which it is possible to attain a good approximation of a sine wave. In this particular topology, the DC-supplies of the converters are isolated from each other.
“11-level Cascaded H-bridge Grid-tied Inverter Interface with Solar Panels”, by Filho et al, Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-Fifth Annual IEEE, Issue Date: 21-25 Feb. 2010, discloses the use of a cascaded H-bridge converter in connection to solar panels. A problem with the system disclosed is the power loss which occurs when transporting solar panel energy from the respective solar panel to the corresponding H-bridge converter.